With the advancement in scientific technologies and the modularization and miniaturization of camera lens, it is now possible to produce digital cameras having a very small volume, and most of currently available mobile phones are provided with the function of a digital camera. In a miniature lens, there are many different auto-focusing driving mechanisms. Among others, voice coil motor (VCM) is the currently most widely adopted auto-focusing driving mechanism. The VCM has the advantages of small volume, low power consumption, accurately actuated displacement, and cost-effective, and is therefore very suitable for short-distance driving in miniature lens auto-focusing.
FIG. 1 schematically shows the basic principle of lens focusing. In a general focusing unit 10, there are included a lens assembly 11 and a photo sensor 12. With the lens assembly 11, light reflected from an object can form an image on the photo sensor 12. In the case a distance between the lens assembly 11 and the photo sensor 12 is fixed, that is, the lens assembly 11 is a fixed focal lens, only the object located more than two to three meters away from the lens can be clearly shown on the camera. If it is desired to own the macro shooting function, it is necessary to use an additional lens focusing unit to displace the lens assembly, so as to change the distance between the lens assembly and the photo sensor and thereby achieve the purpose of focusing. When the lens assembly is provided with the zoom function, multiple lens groups inside the lens assembly must also be displaced corresponding to the changes in zoom ratio. In this case, the focusing unit must also be included in the lens module to enable the displacement of the lens groups.
In the conventional focusing mechanism, the lens assembly is displaced mainly via a manually controlled mechanism, and is therefore not so convenient for operation. It is therefore tried by the inventor to develop an electromagnetically driven lens focusing mechanism, which not only has simplified design and improved assembling process to enable reduced manufacturing cost, but also overcomes the drawbacks in the conventional lens focusing mechanism, and can be advantageously applied to mobile phone, notebook computer, personal digital assistant (PDA), etc.